Method for forming nozzle chamber of inkjet printhead

ABSTRACT

A method for forming a nozzle chamber of an inkjet printhead includes the steps of depositing a sacrificial layer on a wafer substrate; etching the sacrificial layer to define a deposition area for forming sidewalls of the nozzle chamber; depositing a structural layer over the sacrificial layer and into the deposition area; etching the structural layer to define an ink ejection port and a plurality of etchant holes, the etchant holes being etched to a dimension for facilitating the establishment of sufficient surface tension across the etchant hole to restrict egress of ink therethrough from the nozzle chamber; and etching away the sacrificial layer using a sacrificial etchant, the sacrificial etchant being applied to the sacrificial layer via the etchant holes.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a Continuation of U.S. application Ser. No.12/983,799 filed on Jan. 3, 2011, which is a Continuation of U.S.application Ser. No. 12/500,595 filed Jul. 9, 2009, now issued U.S. Pat.No. 7,891,779 which is a Continuation of U.S. application Ser. No.12/017,305 filed Jan. 21, 2008, now issued U.S. Pat. No. 7,568,791,which is a Continuation of U.S. application Ser. No. 10/636,274 filed onAug. 8, 2003, now issued U.S. Pat. No. 7,347,952, which is a Divisionalof U.S. application Ser. No. 10/183,174 filed on Jun. 28, 2002, nowissued U.S. Pat. No. 6,648,453 which is a Continuation-In-Part of U.S.application Ser. No. 09/112,767 filed on Jul. 10, 1998, now issued U.S.Pat. No. 6,416,167, the entire contents of which are herein incorporatedby reference.

FIELD OF THE INVENTION

The present invention relates to ink jet printing. In particular, theinvention relates to an inkjet printhead chip with predeterminedmicro-electromechanical systems height.

BACKGROUND OF THE INVENTION

Many different types of printing have been invented, a large number ofwhich are presently in use. Known forms of printers have a variety ofmethods for marking the print media with a relevant marking media.Commonly used forms of printing include offset printing, laser printingand copying devices, dot matrix type impact printers, thermal paperprinters, film recorders, thermal wax printers, dye sublimation printersand ink jet printers both of the drop on demand and continuous flowtype. Each type of printer has its own advantages and problems whenconsidering cost, speed, quality, reliability, simplicity ofconstruction and operation etc.

In recent years, the field of ink jet printing, wherein each individualpixel of ink is derived from one or more ink nozzles, has becomeincreasingly popular primarily due to its inexpensive and versatilenature.

Many different techniques of ink jet printing have been invented. For asurvey of the field, reference is made to an article by J Moore,“Non-Impact Printing: Introduction and Historical Perspective”, OutputHard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).

Ink Jet printers themselves come in many different forms. Theutilization of a continuous stream of ink in ink jet printing appears todate back to at least 1929 wherein U.S. Pat. No. 1,941,001 by Hanselldiscloses a simple form of continuous stream electro-static ink jetprinting.

U.S. Pat. No. 3,596,275 by Sweet also discloses a process of acontinuous ink jet printing including the step wherein the ink jetstream is modulated by a high frequency electro-static field so as tocause drop separation. This technique is still utilized by severalmanufacturers including Elmjet and Scitex (see also U.S. Pat. No.3,373,437 by Sweet et al)

Piezoelectric ink jet printers are also one form of commonly utilizedink jet printing device. Piezoelectric systems are disclosed by Kyseret. al. in U.S. Pat. No. 3,946,398 (1970) which utilizes a diaphragmmode of operation, by Zolten in U.S. Pat. No. 3,683,212 (1970) whichdiscloses a squeeze mode of operation of a piezoelectric crystal, Stemmein U.S. Pat. No. 3,747,120 (1972) discloses a bend mode of piezoelectricoperation, Howkins in U.S. Pat. No. 4,459,601 discloses a piezoelectricpush mode actuation of the ink jet stream and Fischbeck in U.S. Pat. No.4,584,590 which discloses a shear mode type of piezoelectric transducerelement.

Recently, thermal ink jet printing has become an extremely popular formof ink jet printing. The ink jet printing techniques include thosedisclosed by Endo et al in GB 2007162 (1979) and Vaught et al in U.S.Pat. No. 4,490,728. Both the aforementioned references disclose ink jetprinting techniques rely upon the activation of an electrothermalactuator which results in the creation of a bubble in a constrictedspace, such as a nozzle, which thereby causes the ejection of ink froman aperture connected to the confined space onto a relevant print media.Printing devices utilizing the electro-thermal actuator are manufacturedby manufacturers such as Canon and Hewlett Packard.

As can be seen from the foregoing, many different types of printingtechnologies are available. Ideally, a printing technology should have anumber of desirable attributes. These include inexpensive constructionand operation, high-speed operation, safe and continuous long-termoperation etc. Each technology may have its own advantages anddisadvantages in the areas of cost, speed, quality, reliability, powerusage, simplicity of construction operation, durability and consumables.

In the parent application, U.S. Ser. No. 09/112,767, there is discloseda printing technology that is based on micro-electromechanical systems(MEMS) devices. In particular there is disclosed a printing mechanismthat incorporates a MEMS device. There is also disclosed a method offabricating such a mechanism.

The fabrication of MEMS devices is based on integrated circuitfabrication techniques. Very generally, a sacrificial material isdeposited on a wafer substrate. A functional layer is then deposited onthe sacrificial material. The functional layer is patterned to form aMEMS component. The sacrificial layer is then removed to free the MEMScomponent.

Applicant has found that topography of a MEMS chip is very important.The components are required to move. It follows that the topography mustbe such that sufficient clearance is provided for movement of thecomponents. This means that such features as nozzle chambers must bedeep enough to provide for functional movement of an actuator positionedin the nozzle chamber.

There are, however, problems associated with deep topography. Thisproblem is illustrated in FIGS. 42 and 43 of the drawings. In FIG. 42there is shown a substrate 1 with a layer of sacrificial material 2positioned on the substrate 1.

One problem is immediately apparent. It is extremely difficult toachieve a uniform deposition on side walls 2 and a floor 3 of the cavity4. The fluid dynamics of the deposition process is the primary reasonfor this. As a result, a portion of the sacrificial material within thecavity 4 tends to taper in to the side walls 2.

Accurate etching of the sacrificial material relies on a high imagefocus on the layer 2. It will be appreciated that this focus could belost in the cavity 4, due to the depth of the cavity 4. This results inpoor etching within the cavity 4.

Etching is carried out using a device that etches in steps. These areusually 1 micron in depth. It follows that each stepping process removes1 micron of sacrificial material at a time. As can be seen in Figure B,once a required part of the layer 2 has been removed, a part is leftbehind in the cavity 4. This is called a stringer 5. It will beappreciated that the stringer 5 is difficult to remove and is thereforean undesirable result.

The Applicant has conceived the present invention to provide a printheadchip that incorporates MEMS components that are spaced a predetermineddistance from a wafer substrate so that sufficient ink ejection can beachieved. The predetermined distance is such that the chip topographyavoids the problems described above.

SUMMARY OF THE INVENTION

According to an aspect of the present disclosure, a method for forming anozzle chamber of an inkjet printhead comprises depositing a sacrificiallayer on a wafer substrate; etching the sacrificial layer to define adeposition area for forming sidewalls of the nozzle chamber; depositinga structural layer over the sacrificial layer and into the depositionarea; etching the structural layer to define an ink ejection port and aplurality of etchant holes, the etchant holes being etched to adimension for facilitating the establishment of sufficient surfacetension across the etchant hole to restrict egress of ink therethroughfrom the nozzle chamber; and etching away the sacrificial layer using asacrificial etchant, the sacrificial etchant being applied to thesacrificial layer via the etchant holes.

BRIEF DESCRIPTION OF THE DRAWINGS

Notwithstanding any other forms, which may fall within the scope of thepresent invention, preferred forms of the invention will now bedescribed, by way of example only, with reference to the accompanyingdrawings in which:

FIGS. 1-3 illustrate basic operation of the preferred embodiments ofnozzle arrangements of a printhead chip of the invention.

FIG. 4 is a sectional view of one embodiment of a nozzle arrangement ofa printhead chip of the invention.

FIG. 5 is an exploded perspective view of the nozzle arrangement of FIG.4.

FIGS. 6-15 are cross-sectional views of the printhead chip of theinvention illustrating successive steps in the fabrication of theprinthead chip according to a method of the invention.

FIG. 16 illustrates a top view of the printhead chip of the invention.

FIG. 17 is a legend of the materials used in a method of the inventiondescribed with reference to FIGS. 18 to 29.

FIG. 18 to FIG. 29 illustrate sectional views of the manufacturing stepsin one form of construction of an ink jet printhead having nozzlearrangements of the invention.

FIG. 30 shows a three dimensional, schematic view of a nozzlearrangement for an ink jet printhead in accordance with anotherembodiment of the invention.

FIGS. 31 to 33 show a three dimensional, schematic illustration of anoperation of the nozzle arrangement of FIG. 30.

FIG. 34 shows a three dimensional view of another ink jet printhead chipaccording to the invention.

FIG. 35 shows, on an enlarged scale, part of the ink jet printhead chipof FIG. 34.

FIG. 36 shows a three dimensional view of the ink jet printhead chipwith a nozzle guard.

FIGS. 37A to 37R show three-dimensional views of steps in thefabrication of a nozzle arrangement of the ink jet printhead chip.

FIGS. 38A to 38R show sectional side views of the fabrication steps ofFIGS. 37A to 37R.

FIGS. 39A to 39K show layouts of masks used in various steps in thefabrication process.

FIGS. 40A to 40C show three-dimensional views of an operation of thenozzle arrangement fabricated according to the method of FIGS. 37 and38.

FIGS. 41A to 41C show sectional side views of an operation of the nozzlearrangement fabricated according to the method of FIGS. 37 and 38.

FIG. 42 is a schematic diagram indicating problems associated with deeptopography in a printed chip, as set out in the background of theinvention.

FIG. 43 is a schematic diagram indicating problems associated with deeptopography in a printhead chip, as set out in the background of theinvention.

DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS

In the preferred embodiments of the invention, a drop on demand ink jetnozzle arrangement is provided which allows for the ejection of ink ondemand by means of a thermal actuator which operates to eject the inkfrom a nozzle chamber. The nozzle chamber is formed directly over an inksupply channel thereby allowing for an extremely compact form of nozzlearrangement. The extremely compact form of nozzle arrangement allows forminimal area to be taken up by a printing mechanism thereby resulting inimproved economics of fabrication.

Turning initially to FIGS. 1-3, the operation of the preferredembodiment of the nozzle arrangement is now described. In FIG. 1, thereis illustrated a sectional view of two ink jet nozzle arrangements 10,11 which are formed on a silicon wafer 12 which includes a series ofthrough-wafer ink supply channels 13.

Located over a portion of the wafer 12 and over the ink supply channel13 is a thermal actuator 14, which is actuated so as to eject ink from acorresponding nozzle chamber. The actuator 14 is placed substantiallyover the ink supply channel 13 as a cantilever (see FIGS. 1-3). In thequiescent position, the ink fills the nozzle chamber and an ink meniscus15 forms across an ink ejection port 35 of the chamber.

The actuator 14 is spaced between 6 microns and 10 microns above thewafer 12.

When it is desired to eject a drop from the chamber, the thermalactuator 14 is activated by passing a current through the actuator 14.The actuation causes the actuator 14 to rapidly bend upwards asindicated in FIG. 2. The movement of the actuator 14 results in anincrease in the ink pressure around an ejection port 35 (FIG. 4) of thechamber, which in turn causes, a significant bulging of the meniscus 15and a flow of ink out of the nozzle chamber. The actuator 14 can beconstructed so as to impart sufficient momentum to the ink to cause thedirect ejection of a drop.

As indicated in FIG. 3, the activation of actuator 14 can be timed so asto turn the actuation current off at a predetermined point. This causesthe return of the actuator 14 to its original position thereby resultingin a consequential backflow of ink in the direction of an arrow 17 intothe chamber. A body of ink 18 necks and separates and continues towardsoutput media, such as paper, for printing. The actuator 14 then returnsto its quiescent position and surface tension effects result in arefilling of the nozzle chamber via the ink supply channel 13 as aconsequence of surface tension effects on the meniscus 15. In time, thecondition of the ink returns to that depicted in FIG. 1.

In FIGS. 4 and 5, there is illustrated the structure of a single nozzlearrangement 10 in more detail. FIG. 4 is a part sectional view whileFIG. 5 shows a corresponding exploded perspective view.

Many ink jet nozzle arrangements are formed at a time, on a selectedwafer base 12 utilizing standard semi-conductor processing techniques inaddition to micro-machining and micro-fabrication process technologyfurther details of this form of fabrication are set out in furtherdetail further on in this specification.

A CMOS drive circuitry layer 20 is formed on the wafer 12. The CMOSlayer 20 can, in accordance with standard techniques, includemulti-level metal layers sandwiched between oxide layers and preferablyat least a two level metal process is utilized. In order to reduce thenumber of necessary processing steps, the masks utilized include areasthat provide for a build up of an aluminum barrier 21 which can beconstructed from a first level 22 of aluminum and second level 23 ofaluminum. Additionally, aluminum portions 24 are provided which defineelectrical contacts to a subsequent heater layer. The aluminum barrier21 is important for providing an effective barrier to the possiblesubsequent etching of the oxide within the CMOS layer 20 when asacrificial etchant is utilized in the construction of the nozzlearrangement 10 with the etchable material preferably being glass layers.

A nitride passivation layer 26 is formed on the CMOS layer 20 to protectthe lower CMOS layers from sacrificial etchants and ink erosion. Abovethe nitride layer 26 there is formed a gap 28 in which an air bubbleforms during operation. The gap 28 can be constructed by laying down asacrificial layer and subsequently etching the gap 28 as will beexplained hereinafter. The air gap 28 is between 6 microns and 10microns thick.

On top of the air gap 28 is constructed a polytetrafluroethylene (PTFE)layer 29 which comprises a gold serpentine heater layer 30 sandwichedbetween two PTFE layers. The gold heater layer 30 is constructed in aserpentine form to allow it to expand on heating. The heater layer 30and PTFE layer 29 together comprise the thermal actuator 14 of FIG. 1.

The outer PTFE layer 29 has an extremely high coefficient of thermalexpansion (approximately 770×10⁻⁶, or around 380 times that of silicon).The PTFE layer 29 is also normally highly hydrophobic which results inan air bubble being formed under the actuator in the gap 28 due toout-gassing etc. The top PTFE surface layer is treated so as to make ithydrophilic in addition to those areas around the ink supply channel 13.This can be achieved with a plasma etch in an ammonia atmosphere. Theheater layer 30 is also formed within the lower portion of the PTFElayer.

The heater layer 30 is connected at ends e.g. 31 to the lower CMOS drivelayer 20 that contains the drive circuitry (not shown). For operation ofthe actuator 14, a current is passed through the gold heater element 30that heats the bottom surface of the actuator 14. The bottom surface ofactuator 14, in contact with the air bubble remains heated while any topsurface heating is carried away by the exposure of the top surface ofactuator 14 to the ink within a chamber 32. Hence, the bottom PTFE layerexpands more rapidly resulting in a general rapid upward bending ofactuator 14 (as illustrated in FIG. 2) that consequentially causes theejection of ink from the ink ejection port 35.

Turning off the current to the heater layer 30 can deactivate theactuator 14. This will result in a return of the actuator 14 to its restposition.

On top of the actuator 14 are formed nitride side wall portions 33 and atop wall portion 34. The wall portions 33 and the top portions 34 can beformed via a dual damascene process utilizing a sacrificial layer. Thetop wall portion 34 is etched to define the ink ejection port 35 inaddition to a series of etchant holes 36 which are of a relatively smalldiameter and allow for effective etching of lower sacrificial layerswhen utilizing a sacrificial etchant. The etchant holes 36 are madesmall enough such that surface tension effects restrict thepossibilities of ink being ejected from the chamber 32 via the etchantholes 36 rather than the ejection port 35.

The various steps involved in the construction of an array of ink jetnozzle arrangements are explained in FIGS. 6 to 15.

1. Turning initially to FIG. 6, the starting position comprises asilicon wafer 12 including a CMOS layer 20 which has nitride passivationlayer 26 and which is surface finished with a chemical-mechanicalplanarization process.

2. The nitride layer is masked and etched as illustrated in FIG. 7 so asto define portions of the nozzle arrangement and areas forinterconnection between any subsequent heater layer and a lower CMOSlayer.

3. Next, a sacrificial oxide layer is deposited, masked and etched asindicated in FIG. 8 with the oxide layer being etched in those areaswhere a subsequent heater layer electronically contacts the lowerlayers.

4. As illustrated in FIG. 9, a 1 micron layer of PTFE is deposited andfirst masked and etched for the heater contacts to the lower CMOS layerand then masked and etched for the heater shape.

5. Next, as illustrated in FIG. 10, the gold heater layer 30, 31 isdeposited. Due to the fact that it is difficult to etch gold, the layercan be conformally deposited and subsequently portions removed utilizingchemical mechanical planarization so as to leave those portionsassociated with the heater element. The processing steps 4 and 5basically comprise a dual damascene process.

6. Next, a top PTFE layer is deposited and masked and etched down to thesacrificial layer as illustrated in FIG. 11 so as to define the heatershape. Subsequently, the surface of the PTFE layer is plasma processedso as to make it hydrophilic. Suitable processing can exclude plasmadamage in an ammonia atmosphere. Alternatively, the surface could becoated with a hydrophilic material.

7. A further sacrificial layer is then deposited and etched asillustrated in FIG. 12 so as to form the structure for the nozzlechamber. The sacrificial layer is then masked and etched in order todefine a deposition area for the nozzle chamber walls.

8. As illustrated in FIG. 13, the nozzle chamber is formed byconformally depositing three microns of nitride and etching a masknozzle rim to a depth of one micron for the nozzle rim (the etched depthnot being overly time critical). Subsequently, a mask is utilized toetch the ink ejection port 35 in addition to the sacrificial layeretchant holes 36.

9. As illustrated in FIG. 14, the backside of the wafer is masked forthe ink channels and plasma etched through the wafer. A suitable plasmaetching process can include a deep anisotropic trench etching systemsuch as that available from SDS Systems Limited (See) “Advanced SiliconEtching Using High Density Plasmas” by J. K. Bhardwaj, H. Ashraf, page224 of Volume 2639 of the SPIE Proceedings in Micro Machining and MicroFabrication Process Technology).

10. As illustrated in FIG. 15, the sacrificial layers are etched awayutilizing a sacrificial etchant such as hydrochloric acid. Subsequently,the portion underneath the actuator that is around the ink channel isplasma processed through the backside of the wafer to make the panel endhydrophilic.

Subsequently, the wafer can be separated into separate printheads andeach printhead is bonded into an injection moulded ink supply channeland the electrical signals to the chip can be tape automated bonded(TAB) to the printhead for subsequent testing. FIG. 16 illustrates a topview of nozzle arrangement constructed on a wafer so as to provide forpagewidth multicolor output.

One form of detailed manufacturing process that can be used to fabricatemonolithic ink jet printheads operating in accordance with theprinciples taught by the present embodiment can proceed utilizing thefollowing steps:

1. Using a double sided polished wafer, Complete drive transistors, datadistribution, and timing circuits using a 0.5 micron, one poly, 2 metalCMOS process. This step is shown in FIG. 18. For clarity, these diagramsmay not be to scale, and may not represent a cross section though anysingle plane of the nozzle. FIG. 17 is a key to representations ofvarious materials in these manufacturing diagrams, and those of othercross-referenced ink jet configurations.

2. Deposit 1 micron of low stress nitride. This acts as a barrier toprevent ink diffusion through the silicon dioxide of the chip surface.

3. Deposit 3 microns of sacrificial material (e.g. polyimide).

4. Etch the sacrificial layer using Mask 1. This mask defines theactuator anchor point. This step is shown in FIG. 19.

5. Deposit 0.5 microns of PTFE.

6. Etch the PTFE, nitride, and CMOS passivation down to second levelmetal using Mask 2. This mask defines the heater vias. This step isshown in FIG. 20.

7. Deposit and pattern resist using Mask 3. This mask defines theheater.

8. Deposit 0.5 microns of gold (or other heater material with a lowYoung's modulus) and strip the resist. Steps 7 and 8 form a lift-offprocess. This step is shown in FIG. 21.

9. Deposit 1.5 microns of PTFE.

10. Etch the PTFE down to the sacrificial layer using Mask 4. This maskdefines the actuator and the bond pads. This step is shown in FIG. 22.

11. Wafer probe. All electrical connections are complete at this point,and the chips are not yet separated.

12. Plasma process the PTFE to make the top and side surfaces of theactuator hydrophilic. This allows the nozzle chamber to fill bycapillarity.

13. Deposit 10 microns of sacrificial material.

14. Etch the sacrificial material down to nitride using Mask 5. Thismask defines the nozzle chamber. This step is shown in FIG. 23.

15. Deposit 3 microns of PECVD glass. This step is shown in FIG. 24.

16. Etch to a depth of 1 micron using Mask 6. This mask defines a rim ofthe ejection port. This step is shown in FIG. 25.

17. Etch down to the sacrificial layer using Mask 7. This mask definesthe ink ejection port and the sacrificial etch access holes. This stepis shown in FIG. 26.

18. Back-etch completely through the silicon wafer (with, for example,an ASE Advanced Silicon Etcher from Surface Technology Systems) usingMask 8. This mask defines the ink inlets that are etched through thewafer. The wafer is also diced by this etch. This step is shown in FIG.27.

19. Back-etch the CMOS oxide layers and subsequently deposited nitridelayers and sacrificial layer through to PTFE using the back-etchedsilicon as a mask.

20. Plasma process the PTFE through the back-etched holes to make thetop surface of the actuator hydrophilic. This allows the nozzle chamberto fill by capillarity, but maintains a hydrophobic surface underneaththe actuator. This hydrophobic section causes an air bubble to betrapped under the actuator when the nozzle is filled with a water-basedink. This bubble serves two purposes: to increase the efficiency of theheater by decreasing thermal conduction away from the heated side of thePTFE, and to reduce the negative pressure on the back of the actuator.

21. Etch the sacrificial material. The nozzle arrangements are cleared,the actuators freed, and the chips are separated by this etch. This stepis shown in FIG. 28.

22. Mount the printheads in their packaging, which may be a moldedplastic former incorporating ink channels that supply the appropriatecolor ink to the ink inlets at the back of the wafer.

23. Connect the printheads to their interconnect systems. For a lowprofile connection with minimum disruption of airflow, TAB may be used.Wire bonding may also be used if the printer is to be operated withsufficient clearance to the paper.

24. Hydrophobize the front surface of the printheads.

25. Fill the completed printheads with ink and test them. A fillednozzle is shown in FIG. 29.

In FIG. 30 of the drawings, a nozzle arrangement, in accordance with afurther embodiment of the invention, is designated generally by thereference numeral 110. An ink jet printhead chip of the invention has aplurality of nozzle arrangements 110 arranged in an array 114 (FIGS. 34and 35) on a silicon substrate 116. The array 114 will be described ingreater detail below.

The arrangement 110 includes a silicon substrate or wafer 116 on which adielectric layer 118 is deposited. A CMOS passivation layer 120 isdeposited on the dielectric layer 118.

Each nozzle arrangement 110 includes a nozzle 122 defining a nozzleopening 124, a connecting member in the form of a lever arm 126 and anactuator 128. The lever arm 126 connects the actuator 128 to the nozzle122.

As shown in greater detail in FIGS. 31 to 33 of the drawings, the nozzle122 comprises a crown portion 130 with a skirt portion 132 dependingfrom the crown portion 130. The skirt portion 132 forms part of aperipheral wall of a nozzle chamber 134 (FIGS. 31 to 33 of thedrawings). The nozzle opening 124 is in fluid communication with thenozzle chamber 134. It is to be noted that the nozzle opening 124 issurrounded by a raised rim 136 that “pins” a meniscus 138 (FIG. 31) of abody of ink 140 in the nozzle chamber 134.

The skirt portion 132 is positioned between 6 microns and 10 micronsabove the CMOS passivation layer 120.

An ink inlet aperture 142 (shown most clearly in FIG. 35 of the drawing)is defined in a floor 146 of the nozzle chamber 134. The aperture 142 isin fluid communication with an ink inlet channel 148 defined through thesubstrate 116.

A wall portion 150 bounds the aperture 142 and extends upwardly from thefloor portion 146. The skirt portion 132, as indicated above, of thenozzle 122 defines a first part of a peripheral wall of the nozzlechamber 134 and the wall portion 150 defines a second part of theperipheral wall of the nozzle chamber 134.

The wall 150 has an inwardly directed lip 152 at its free end thatserves as a fluidic seal that inhibits the escape of ink when the nozzle122 is displaced, as will be described in greater detail below. It willbe appreciated that, due to the viscosity of the ink 140 and the smalldimensions of the spacing between the lip 152 and the skirt portion 132,the inwardly directed lip 152 and surface tension function as a seal forinhibiting the escape of ink from the nozzle chamber 134.

The actuator 128 is a thermal bend actuator and is connected to ananchor 154 extending upwardly from the substrate 116 or, moreparticularly, from the CMOS passivation layer 120. The anchor 154 ismounted on conductive pads 156 which form an electrical connection withthe actuator 128.

The actuator 128 comprises a first, active beam 158 arranged above asecond, passive beam 160. In a preferred embodiment, both beams 158 and160 are of, or include, a conductive ceramic material such as titaniumnitride (TiN).

Both beams 158 and 160 have their first ends anchored to the anchor 154and their opposed ends connected to the arm 126. When a current iscaused to flow through the active beam 158 thermal expansion of the beam158 results. As the passive beam 160, through which there is no currentflow, does not expand at the same rate, a bending moment is createdcausing the arm 126 and, hence, the nozzle 122 to be displaceddownwardly towards the substrate 116 as shown in FIG. 32 of thedrawings. This causes an ejection of ink through the nozzle opening 124as shown at 162 in FIG. 32 of the drawings. When the source of heat isremoved from the active beam 158, i.e. by stopping current flow, thenozzle 122 returns to its quiescent position as shown in FIG. 33 of thedrawings.

When the nozzle 122 returns to its quiescent position, an ink droplet164 is formed as a result of the breaking of an ink droplet neck asillustrated at 166 in FIG. 33 of the drawings. The ink droplet 164 thentravels on to the print media such as a sheet of paper. As a result ofthe formation of the ink droplet 164, a “negative” meniscus is formed asshown at 168 in FIG. 33 of the drawings. This “negative” meniscus 168results in an inflow of ink 140 into the nozzle chamber 134 such that anew meniscus 138 (FIG. 31) is formed in readiness for the next ink dropejection from the nozzle arrangement 110.

Referring now to FIGS. 34 and 35 of the drawings, the nozzle array 114is described in greater detail. The array 114 is for a four-colorprinthead. Accordingly, the array 114 includes four groups 170 of nozzlearrangements, one for each color. Each group 170 has its nozzlearrangements 110 arranged in two rows 172 and 174. One of the groups 170is shown in greater detail in FIG. 35 of the drawings.

To facilitate close packing of the nozzle arrangements 110 in the rows172 and 174, the nozzle arrangements 110 in the row 174 are offset orstaggered with respect to the nozzle arrangements 110 in the row 172.Also, the nozzle arrangements 110 in the row 172 are spaced apartsufficiently far from each other to enable the lever arms 126 of thenozzle arrangements 110 in the row 174 to pass between adjacent nozzles122 of the arrangements 110 in the row 172. It is to be noted that eachnozzle arrangement 110 is substantially dumbbell shaped so that thenozzles 122 in the row 172 nest between the nozzles 122 and theactuators 128 of adjacent nozzle arrangements 110 in the row 174.

Further, to facilitate close packing of the nozzles 122 in the rows 172and 174, each nozzle 122 is substantially hexagonally shaped.

It will be appreciated by those skilled in the art that, when thenozzles 122 are displaced towards the substrate 116, in use, due to thenozzle opening 124 being at a slight angle with respect to the nozzlechamber 134 ink is ejected slightly off the perpendicular. It is anadvantage of the arrangement shown in FIGS. 34 and 35 of the drawingsthat the actuators 128 of the nozzle arrangements 110 in the rows 172and 174 extend in the same direction to one side of the rows 172 and174. Hence, the ink droplets ejected from the nozzles 122 in the row 172and the ink droplets ejected from the nozzles 122 in the row 174 areparallel to one another resulting in an improved print quality.

Also, as shown in FIG. 34 of the drawings, the substrate 116 has bondpads 176 arranged thereon which provide the electrical connections, viathe pads 156, to the actuators 128 of the nozzle arrangements 110. Theseelectrical connections are formed via the CMOS layer (not shown).

Referring to FIG. 36 of the drawings, a development of the invention isshown. With reference to the previous drawings, like reference numeralsrefer to like parts, unless otherwise specified.

In this development, a nozzle guard 180 is mounted on the substrate 116of the array 114. The nozzle guard 180 includes a body member 182 havinga plurality of passages 184 defined therethrough. The passages 184 arein register with the nozzle openings 124 of the nozzle arrangements 110of the array 114 such that, when ink is ejected from any one of thenozzle openings 124, the ink passes through the associated passage 184before striking the print media.

The body member 182 is mounted in spaced relationship relative to thenozzle arrangements 110 by limbs or struts 186. One of the struts 186has air inlet openings 188 defined therein.

In use, when the array 114 is in operation, air is charged through theinlet openings 188 to be forced through the passages 184 together withink travelling through the passages 184.

The ink is not entrained in the air as the air is charged through thepassages 184 at a different velocity from that of the ink droplets 164.For example, the ink droplets 164 are ejected from the nozzles 122 at avelocity of approximately 3 m/s. The air is charged through the passages184 at a velocity of approximately 1 m/s.

The purpose of the air is to maintain the passages 184 clear of foreignparticles. A danger exists that these foreign particles, such as dustparticles, could fall onto the nozzle arrangements 110 adverselyaffecting their operation. With the provision of the air inlet openings88 in the nozzle guard 180 this problem is, to a large extent, obviated.

The nozzle arrangements 110 are configured to define a relatively flattopography for the printhead chip. This is emphasized by the fact thatthe skirt portion 132 of each nozzle arrangement is between 6 micronsand 10 microns from the ink passivation layer 120. The problemsassociated with having deep topography are set out in the Background tothe Invention above. It follows that a particular advantage of theconfiguration of the nozzle arrangements 110 is that these problems areaddressed.

Referring now to FIGS. 37 to 39 of the drawings, a process formanufacturing the nozzle arrangements 110 is described.

Starting with the silicon substrate or wafer 116, the dielectric layer118 is deposited on a surface of the wafer 116. The dielectric layer 118is in the form of approximately 1.5 microns of CVD oxide. Resist is spunon to the layer 118 and the layer 118 is exposed to mask 200 and issubsequently developed.

After being developed, the layer 118 is plasma etched down to thesilicon layer 116. The resist is then stripped and the layer 118 iscleaned. This step defines the ink inlet aperture 142.

In FIG. 37 b of the drawings, approximately 0.8 microns of aluminum 202is deposited on the layer 118. Resist is spun on and the aluminum 202 isexposed to mask 204 and developed. The aluminum 202 is plasma etcheddown to the oxide layer 118, the resist is stripped and the device iscleaned. This step provides the bond pads and interconnects to the inkjet actuator 128. This interconnect is to an NMOS drive transistor and apower plane with connections made in the CMOS layer (not shown).

Approximately 0.5 microns of PECVD nitride is deposited as the CMOSpassivation layer 120. Resist is spun on and the layer 120 is exposed tomask 206 whereafter it is developed. After development, the nitride isplasma etched down to the aluminum layer 202 and the silicon layer 116in the region of the inlet aperture 142. The resist is stripped and thedevice cleaned.

A layer 208 of a sacrificial material is spun on to the layer 120. Thelayer 208 is 6 microns of photosensitive polyimide or approximately 4 μmof high temperature resist. The layer 208 is softbaked and is thenexposed to mask 210 whereafter it is developed. The layer 208 is thenhardbaked at 400° C. for one hour where the layer 208 is comprised ofpolyimide or at greater than 300° C. where the layer 208 is hightemperature resist. It is to be noted in the drawings that thepattern-dependent distortion of the polyimide layer 208 caused byshrinkage is taken into account in the design of the mask 210.

In the next step, shown in FIG. 37 e of the drawings, a secondsacrificial layer 212 is applied. The layer 212 is either 2 μm ofphotosensitive polyimide, which is spun on, or approximately 1.3 μm ofhigh temperature resist. The layer 212 is softbaked and exposed to mask214. After exposure to the mask 214, the layer 212 is developed. In thecase of the layer 212 being polyimide, the layer 212 is hardbaked at400° C. for approximately one hour. Where the layer 212 is resist, it ishardbaked at greater than 300° C. for approximately one hour.

A 0.2 micron multi-layer metal layer 216 is then deposited. Part of thislayer 216 forms the passive beam 160 of the actuator 128.

It is to be noted that at this stage, there is between 5.3 microns and 8microns of sacrificial material forming a deposit area for the passivebeam 160 of the actuator 128.

The layer 216 is formed by sputtering 1,000 Å of titanium nitride (TiN)at around 300° C. followed by sputtering 50 Å of tantalum nitride (TaN).A further 1,000 Å of TiN is sputtered on followed by 50 Å of TaN and afurther 1,000 Å of TiN.

Other materials that can be used instead of TiN are TiB₂, MoSi₂ or(Ti,Al)N.

The layer 216 is then exposed to mask 218, developed and plasma etcheddown to the layer 212 whereafter resist, applied for the layer 216, iswet stripped taking care not to remove the cured layers 208 or 212.

A third sacrificial layer 220 is applied by spinning on 4 μm ofphotosensitive polyimide or approximately 2.6 μm high temperatureresist. The layer 220 is softbaked whereafter it is exposed to mask 222.The exposed layer is then developed followed by hardbaking. In the caseof polyimide, the layer 220 is hardbaked at 400° C. for approximatelyone hour or at greater than 300° C. where the layer 220 comprisesresist.

A second multi-layer metal layer 224 is applied to the layer 220. Theconstituents of the layer 224 are the same as the layer 216 and areapplied in the same manner. It will be appreciated that both layers 216and 224 are electrically conductive layers.

The layer 224 is exposed to mask 226 and is then developed. The layer224 is plasma etched down to the polyimide or resist layer 220whereafter resist applied for the layer 224 is wet stripped taking carenot to remove the cured layers 208, 212 or 220. It will be noted thatthe remaining part of the layer 224 defines the active beam 158 of theactuator 128.

A fourth sacrificial layer 228 is applied by spinning on 4 μm ofphotosensitive polyimide or approximately 2.6 μm of high temperatureresist. The layer 228 is softbaked, exposed to the mask 230 and is thendeveloped to leave the island portions as shown in FIG. 9 k of thedrawings. The remaining portions of the layer 228 are hardbaked at 400°C. for approximately one hour in the case of polyimide or at greaterthan 300° C. for resist.

As shown in FIG. 37I of the drawing a high Young's modulus dielectriclayer 232 is deposited. The layer 232 is constituted by approximately 1μm of silicon nitride or aluminum oxide. The layer 232 is deposited at atemperature below the hardbaked temperature of the sacrificial layers208, 212, 220, 228. The primary characteristics required for thisdielectric layer 232 are a high elastic modulus, chemical inertness andgood adhesion to TiN.

A fifth sacrificial layer 234 is applied by spinning on 2 μm ofphotosensitive polyimide or approximately 1.3 μm of high temperatureresist. The layer 234 is softbaked, exposed to mask 236 and developed.The remaining portion of the layer 234 is then hardbaked at 400° C. forone hour in the case of the polyimide or at greater than 300° C. for theresist.

The dielectric layer 232 is plasma etched down to the sacrificial layer228 taking care not to remove any of the sacrificial layer 234.

This step defines the nozzle opening 124, the lever arm 126 and theanchor 154 of the nozzle arrangement 110.

A high Young's modulus dielectric layer 238 is deposited. This layer 238is formed by depositing 0.2 μm of silicon nitride or aluminum nitride ata temperature below the hardbaked temperature of the sacrificial layers208, 212, 220 and 228.

Then, as shown in FIG. 37 p of the drawings, the layer 238 isanisotropically plasma etched to a depth of 0.35 microns. This etch isintended to clear the dielectric from the entire surface except the sidewalls of the dielectric layer 232 and the sacrificial layer 234. Thisstep creates the nozzle rim 136 around the nozzle opening 124, which“pins” the meniscus of ink, as described above.

An ultraviolet (UV) release tape 240 is applied. 4 μm of resist is spunon to a rear of the silicon wafer 116. The wafer 116 is exposed to mask242 to back etch the wafer 116 to define the ink inlet channel 148. Theresist is then stripped from the wafer 116.

A further UV release tape (not shown) is applied to a rear of the wafer16 and the tape 240 is removed. The sacrificial layers 208, 212, 220,228 and 234 are stripped in oxygen plasma to provide the final nozzlearrangement 110 as shown in FIGS. 37 r and 38 r of the drawings. Forease of reference, the reference numerals illustrated in these twodrawings are the same as those in FIG. 30 of the drawings to indicatethe relevant parts of the nozzle arrangement 110. FIGS. 40 and 41 showthe operation of the nozzle arrangement 110, manufactured in accordancewith the process described above with reference to FIGS. 37 and 38, andthese figures correspond to FIGS. 31 to 33 of the drawings.

It would be appreciated by a person skilled in the art that numerousvariations and/or modifications may be made to the present invention asshown in the specific embodiments without departing from the spirit orscope of the invention as broadly described. The present embodimentsare, therefore, to be considered in all respects to be illustrative andnot restrictive.

The presently disclosed ink jet printing technology is potentiallysuited to a wide range of printing system including: colour andmonochrome office printers, short run digital printers, high speeddigital printers, offset press supplemental printers, low cost scanningprinters high speed pagewidth printers, notebook computers with inbuiltpagewidth printers, portable colour and monochrome printers, colour andmonochrome copiers, colour and monochrome facsimile machines, combinedprinter, facsimile and copying machines, label printers, large formatplotters, photograph copiers, printers for digital photographic“minilabs”, video printers, PHOTO CD (PHOTO CD is a registered trademark of the Eastman Kodak Company) printers, portable printers for PDAs,wallpaper printers, indoor sign printers, billboard printers, fabricprinters, camera printers and fault tolerant commercial printer arrays.

1. A method for forming a nozzle chamber of an inkjet printhead themethod comprising: depositing a sacrificial layer on a wafer substrate;etching the sacrificial layer to define a deposition area for formingsidewalls of the nozzle chamber; depositing a structural layer over thesacrificial layer and into the deposition area; etching the structurallayer to define an ink ejection port and a plurality of etchant holes,the etchant holes being etched to a dimension for facilitating theestablishment of sufficient surface tension across the etchant hole torestrict egress of ink therethrough from the nozzle chamber; and etchingaway the sacrificial layer using a sacrificial etchant, the sacrificialetchant being applied to the sacrificial layer via the etchant holes. 2.A method according to claim 1, further comprising a step of thinningportions of the structural layer via an etching process to define anozzle rim around the ink ejection port.
 3. A method according to claim2, wherein the step of thinning etches portions of the structural layerby 1 micron.